Molybdenum nickel chromium bonded titanium carbide

ABSTRACT

This invention relates generally to metal cutting bits which consist essentially of titanium carbide bonded with an alloy of molybdenum and nickel. This invention teaches that such cutting bits may be substantially improved for certain types of service by replacing a portion of the nickel with chromium. This addition makes the tool especially resistant to failure by repeated thermal shocks.

United States Patent Humenik, Jr. et al.

[ Apr. 22, 1975 MOLYBDENUM NICI (EL CHROMIUM BONDED TITANIUM CARBIDEInventors: Michael IIumenik, Jr., Allen Park: David Moskowitz,Southfield. both of Mich.

Ford Motor Company, Dearborn. Mich.

Filed: Dec. 22, 1971 Appl. No.: 210,657

Assignee:

US. Cl 29/95 D; 29/95 A; 29/182.7 Int. Cl. B26d 1/00 Field of Search82/1 C; 29/l82.7, 95 A,

References Cited UNITED STATES PATENTS Kelly et a1 Q9/1827 X 3.480.41011/1969 Hummer 29/l82.7

3,507,631 4/1970 Yates 29/18' 7 3.551991 1/1971 Reich et 29/l82.8 X3,552.93? l/l971 Mito et al. Q9/1827 Primary Examiner- Leonidas Vlachos-Al!urney, Agenl. 0r Firm-Joseph W. Malleck; Keith L. Zerschling [57]ABSTRACT 3 Claims, 3 Drawing Figures FIG FIG

FIG

MOLYBDENUM NICKEL CHROMIUM BONDED TITANIUM CARBIDE HISTORICALLY Metalcutting bits in which the hard material is titanium carbide and thebonding metal an alloy of molybdenum and nickel have long been known tothe machining fraternity and have enjoyed considerable commericalsuccess. These titanium carbide based bits have replaced to asubstantial extent the tungsten carbide bits which for decades dominatedthe high speed machining field.

These titanium carbide cutting bits have given generally verysatisfactory commerical service and for many purposes result in lowercutting costs than other com petitive materials. Carbide cutting toolstend to fail in roughing or intermittent cuts by a mechanism known asthermal fatigue or thermal cracking. This invention teaches a system bywhich these premature failures due to thermal fatigue or thermalcracking may be largely avoided.

THE INVENTION This invention is predicated upon the fact that thethermal performance of titanium carbide cutting tools can be enormouslyimproved by substituting chromium for a portion of the nickel in thenickel molybdenum binding alloy. Optimum results have been obtained byreplacing between 40 and I percent of the nickel in the bonding alloy bychromium. The chromium will be added to the powder mix before compactionand may be added as elemental chromium. chromium carbide. a solidsolution of chromium carbide in titanium carbide. a nickel alloy. or anymixture of these sources of chromium.

A typical cutting tool produced by this invention comprises 22:5 percentnickel. 10.0 percent molybdenum. five percent chromium with theremainder titanium carbide and incidental impurities. The binding alloyswere added as approximately five micron powder. A titanium carbidepowder composition having the following analysis was chosen as the basematerial:

Free carbon .2 I "/1 Combined carbon l 9.5; Titanium 79.3 Oxygen 19% Thesize analysis of this material as determined by Fisher particle sizeanalysis was 3.67 microns.

The particle size distribution. using the Turbidimeter method ofanalysis. was as follows:

0-5 microns 46.4 weight /2 -H! microns 27.3 weight 71 IU-Zt) microns26.4 weight "/1 The grinding operations were conducted in a Hastelloy Bmill containing titanium carbide base balls. acetone being added toinhibit oxidation ofthe charge during the 96 hour milling period. Aftermilling the acetone was evaporated and four percent wax binder wasadded. Upon drying the powder was pressed in a steel die at a pressureof about l0 tons per square inch.

The cold pressed compacts were presintered in a hydrogen ambient atl.2()0 Fahrenheit for 1 hour to dewax the specimens. Final sintering wasperformed on an inert stool and in an inert ambient at 2.500 Fahrenheitfor l hour in an induction furnace. An absolute pressure of about 0.] to1.0 microns was maintained in the furnace although any suitable inertambient will be satisfactory. Additional suitable inert ambients are dryhydrogen. argon or helium. The sintering temperature is. of course. afunction of sintering time. the time being shortened as the temperatureis raised. In any event the sintering temperature should not exceed2.700 Fahrenheit to avoid substantial grain growth. The time andtemperature of sintering must be adjusted so that the grain size of thetitanium carbide in the finished article is not substantially largerthan approximately five microns.

It is essential that the initial binding alloy contain at least 10percent of molybdenum to take advantage of the ability of this metal tocause alloys containing it to wet the surface of the hard titaniumcarbide particles.

The titanium carbide employed in these cutting tools prior to sinteringshould be effectively free of molybdenum carbides in solid solution.

Since the sintering temperatures employed in the preparation of thecompacts are high enough to permit the constituents of the compacts tocome to equilibrium between the titanium. molybdenum and carbon. itwould appear at first blush to be immaterial whether the molybdenum wereadded as elemental molybdenum. as molybdenum carbide. or as a solidsolution of molybdenum carbide in titanium carbide. However. experiencehas demonstrated that the addition of molybdenum as the carbidedissolved in titanium carbide produces decidedly inferior tools whilethe addition of molybdenum as elemental molybdenum or as molybdenumcarbide not dissolved in titanium carbide produces decidedlysatisfactory tools.

Without being bound by the following seemingly correct explanation ofthe superior performance of the tools of the current invention. themechanism of the improvement appears to be as follows. The performanceof these modified tools is particularly improved in making roughing orintermittent cuts where the actual cutting edge of the tool is rapidlyand intermittently heated and cooled. These thermal excursions of thecutting tool edge are due to the fact that at least a portion of thecutting edge of the tool is out of actual contact with the work duringa. portion of a revolution of the work piece due to casting defects.nonconcentricity of parts of the work piece with the axis of the cuttingmachine. or cutting across depressions deliberately provided such as keyways.

All of the tool edge actually and instantaneously engaged in cuttingbecomes highly heated by cutting friction. As a portion or all of thecutting edge becomes disengaged momentarily from the work it becomesexposed to the quenching effect of the cutting coolant or theself-quenching effect of the adjacent cool parts of the tool. Theserepeated thermal excursions of the tool edge cause the metal to expandand cause stress beyond the yield point resulting in permanentdeformation or strain. These cumulative repeated plastic deformations ofthe tool edge result in premature failure of the tool.

FIG. 1 of the drawings is a slightly magnified photograph of aconventional titanium carbide cutting tool which has failed by repeatedthermal strain. Note the destruction of the working tip of the tool.

FIG. 2 also depicts a conventional titanium carbide cutting tool at anearlier stage of failure. Note that this cutting tool exhibits severethermal cracking and that the cracks are disposed both normal to thecutting edge and parallel to the cutting edge. It is the presence of thecracks parallel to the cutting edge which promotes catastrophic failureof the tool bit. This drawing shows an unmodified titanium base toolcontaining as bonding metals 17.5 percent nickel and nine percentmolybdenum. This particular tool had machined one hundred automotiverear axle pinion gears in a rough turning and facing operation.

FIG. 3 shows the crack pattern obtained on the same base compositionmodified by the presence of chromium. the chromium was present to theextent of percent of the nickel content. This tool was employed in thesame machining operation of the rear axle pinion gears and at the samemachining operation of the rear axle pinion gears and at the time thephotograph was taken had machined two hundred pieces or twice as many asthe tool shown in FIG. 2. Attention is especially invited to the factthat in this tool the thermal cracks are oriented only normally to theedge of the cutting tool instead of normal and parallel to the edge asshown in FIG. 2. The tool in FIG. 3 is still in operable condition. Theabsence of cracks parallel to the edge of the tool makes thedecrepitation of the bit much less likely to occur.

This is an improvement over the invention described and claimed inReissue U.S. Pat. No. 25.815 dated Jul. 6. I965 and the teachingthereofis incorporated herein by reference.

We claim as our invention:

1. An admixture for making a hard sintered metallic cutting tool highlyresistant to thermal shock and wear. comprising:

a. a base particulate constituent consisting essentially of titaniumcarbide and being free of detrimental quantities of nitrides and oxidesand further being essentially free of dissolved molybdenum. molyb-.

denum carbides. chromium. and chromium carbides.

b. a binder constituent comprising l0-50 percent of the admixture andconsisting essentially ofa particulate having elements selected from theiron group. nickel elemental chromium and molybdenum. said elementalchromium being present in the binder as chromium or chromium carbidecompounds or a mixture thereof and being present in a weight amountbetween 10-40 percent of said nickel. and said molybdenum being presentas molybdenum or molybdenum compounds in an amount between 25-70 percentof said nickel.

2. An admixture for making a hard sintered metallic cutting tool highlyresistant to thermal shock and wear. comprising:

a. a base particulate constituent consisting essentially of titaniumcarbide and being free of detrimental quantities of nitrides and oxidesand further being essentially free of dissolved molybdenum andmolybdenum carbides.

b. a binder constituent comprising 10-50 percent of the admixture andconsisting essentially ofa particulate having elemental or combinedforms of nickel. chromium and molybdenum. the chromium form beingpresent in the binder in an amount measured as elemental chromium in therange between l0-40 percent of said nickel form. and said molybdenumform being present in an amount between 25-70 percent of said nickelform and said binder.

3. A sintered metallic cutting tool as in claim 1. in which said tool issintered at a temperature not in excess of 2.700 F. thereby maintainingthegrain size of the titanium carbide base material at a size equal toor less than 5 microns.

1. AN ADMIXTURE FOR MAKING A HARD SINTERED METALLIC CUTTING TOOL HIGHLYRESISTANT TO THERMAL SHOCK AND WEAR, COMPRISING: A. A BASE PARTICULATECONSTITUENT CONSISTING ESSENTIALLY OF TITANIUM CARBIDE AND BEING FREE OFDETRIMENTAL QUANTITIES OF NITRIDES AND OXIDES AND FURTHER BEINGESSENTIALLY FREE OF DISSOLVED MOLYBDENUM, MOLYBDENUM CARBIDES, CHROMIUM,AND CHROMIUM CARBIDES, B. A BINDER CONSTITUENT COMPRISING 10-50 PERCENTOF THE ADMIXTURE AND CONSISTING ESSENTIALLY OF A PARTICULATE HAVINGELEMENTS SELECTED FROM THE IRON GROUP, NICKEL ELEMENTAL CHROMIUM ANDMOLYBDENUM, SAID ELEMENTAL CHROMIUM BEING PRESENT IN THE BINDER ASCHROMIUM OR CHROMIUM CARBIDE COMPOUNDS OR A MIXTURE THEREOF AND BEINGPRESENT IN A WEIGHT AMOUNT BETWEEN 10-40 PERCENT OF SAID NICKEL, ANDSAID MOLYBDENUM BEING PRESENT AS MOLYBDENUM OR MOLYBDENUM COMPOUNDS INAN AMOUNT BETWEEN 25-70 PERCENT OF SAID NICKEL.
 1. An admixture formaking a hard sintered metallic cutting tool highly resistant to thermalshock and wear, comprising: a. a base particulate constituent consistingessentially of titanium carbide and being free of detrimental quantitiesof nitrides and oxides and further being essentially free of dissolvedmolybdenum, molybdenum carbides, chromium, and chromium carbides, b. abinder constituent comprising 10-50 percent of the admixture andconsisting essentially of a particulate having elements selected fromthe iron group, nickel elemental chromium and molybdenum, said elementalchromium being present in the binder as chromium or chromium carbidecompounds or a mixture thereof and being present in a weight amountbetween 10-40 percent of said nickel, and said molybdenum being presentas molybdenum or molybdenum compounds in an amount between 25-70 percentof said nickel.
 2. An admixture for making a hard sintered metalliccutting tool highly resistant to thermal shock and wear, comprising: a.a base particulate constituent consisting essentially of titaniumcarbide and being free of detrimental quantities of nitrides and oxidesand further being essentially free of dissolved molybdenum andmolybdenum carbides, b. a binder constituent comprising 10-50 percent ofthe admixture and consisting essentially of a particulate havingelemental or combined forms of nickel, chromium and molybdenum, thechromium form being present in the binder in an amount measured aselemental chromium in the range between 10-40 percent of said nickelform, and said molybdenum form being present in an amount between 25-70percent of said nickel form and said binder.